Room: ePoster Forums
Purpose: Intra-target dose surrogates such as mean dose and small-volume hot spot doses vary significantly with target size in stereotactic radiosurgery (SRS). Impact of such dosimetric variations and patientsâ€™ treatment histories on the treatment outcome are poorly understood. The current study investigates prognostic value of intra-target dose surrogates and prior treatment characteristics on the local control of large meningiomas treated with Gamma Knife SRS.
Methods: A total of 110 meningioma lesions for 65 patients treated with single fraction SRS at our institution between 1997~2007 were analyzed. Mean prescription dose was 15.0Â±1.5 Gy (Range:12~19Gy). Mean target volume was 5.3Â±4.1 cc (Range:0.51~23.2cc) and mean maximum target diameter was 3.1Â±0.9 cm (Range:2.0~7.2cm). Patients had mean follow-up time of 88 months (Range:3.5~283mo.), in which each lesion was scored for treatment failure versus local control from mean imaging follow up of 81 months (Range:3.5~233mo.). Logistic regression models were constructed to fit binominal outcome of failure (n=30) vs. local control (n=80) with respect to target size, various dose surrogates (Dmean, Dmax, Dâ‚‰â‚…, Dâ‚?â‚€, Dâ‚…, Dâ‚?, etc.), and patients treatment history (prior surgery, prior extra beam radiotherapy (EBRT), or multimodal therapy).
Results: The mean target dose was found to correlate more strongly with Dâ‚… and Dâ‚?â‚€ (RÂ²>0.9) than with large-volume dose surrogates such as Dâ‚‰â‚… (RÂ²<0.7). Large variability in the dose surrogates such as mean target dose (Range:5~28Gy) and Dâ‚?â‚€ (Range:19~34Gy) did not reach statistical significance for the logistic regression curve. The use of prior EBRT was the only statistically significant predictor (p<=0.007) for the model.
Conclusion: Strong inter-dependence between mean target dose and the small-volume dose surrogates is observed. Large variability in the intra-target dose surrogates did not track with the maximum target size in predicting local control for SRS of large meningioma. The prior EBRT history was the only significant factor associated with local control.